Aircraft control apparatus



March 1965 J. H. BALDWIN ETAL AIRCRAFT CONTROL APPARATUS Filed July 23, 1958 13 Sheets-Sheet l RADIO COMMAND LINK 24 g 20 21 A 30 T CARRIER 22 23 27 r TRANS- AUTOMATIC SQSEDR COMPUTERS MITTER M RECEIVER PILOT 25 26 Fig.1

sr'o, COMP,

l A. .j""' Cl Fig/2 DEVELOPED HENRY W. BERRY ROBERT M. MADVIG JOHN H. BALDWIN BY ATTORNEY March 1965 J. H. BALDWIN ETAL 3,175,788

AIRCRAFT CONTROL APPARATUS l3 Sheets-Sheet 2 Filed July 23. 1958 HENRY W BERRY ROBERTM MADVIG 3 4 w m "mm B an 1 /u m M u 5 5 6 7 l r m m m m 2 JOHN H. BALDWIN .LISO

ATTORNEY Fig.6

March 30, 1965 wm ETAL 3,175,788

AIRCRAFT CONTROL APPARATUS l3 Sheets-Sheet 3 Filed July 23, 1958 ROBERT M. MADVIG JOHN H. BALDWIN ATTORNEY Mardl 1965 J. H. BALDWIN ETAL 3,175,788

AIRCRAFT CONTROL APPARATUS l3 Sheets-Sheet 4 Filed July 23 1958 ATTORNEY March 30, 1965 J. H. BALDWIN ETAL 3,175,788.

AIRCRAFT con'rnon APPARATUS Filed July 23. 1958 13 Sheets-Sheet 5 Fig.8

INVERTING i s AMPLIFIER Fig.7

HENRY W. BERRY ROBERT M. MADVIG JOHN H. BALDWIN ATTORNEY ETAL 3,175,788 AIRCRAFT CONTROL APPARATUS March 30, 1965 J. H. BALDWIN 13 Sheets-Sheet 6 Filed July 23. 1958 Ym WDW H AD M N B .A M w .n T YR A EN mum HRJ March 1965 J. H. BALDWIN ETAL 3,175,783

AIRCRAFT CONTROL APPARATUS 13 Sheets-Sheet 7 Filed July 23, 1958 HENRY W. BERRY ROBERT M. MADVIG JOHN H. BALDWIN I March 30, 1965 wm ETAL 3,175,788

AIRCRAFT CONTROL APPARATUS 13 Sheets-Sheet 8 Filed July 25, 1958 March 1965 J. H. BALDWIN ETAL 3,

AIRCRAFT CONTROL APPARATUS Filed July 23, 1958 13 Sheets-Sheet 11 MOTOR CONTROL r AMP 142 JOHN H. BALDWIN ATT RNEY /7T3 1e5 7,64 76g I 766 SPRING 4 ALTITUDE FORCE i, CENTERED SENSOR BALANCE OUTPUT 66 DEVICE I I c 742M HENRY w. BERRY 112 Fig/7 ROBERT M. MADVIG Mardl 30, 1955 J H. BALDWIN ETAL 3,175,788

AIRCRAFT CONTROL APPARATUS Filed July 23. 1958 HENRY W. BERRY ROBERT M. MADVIG JOHN H. BALDWIN M 88. 3 HV m A TORNEY March 1965 J. H.BALDWIN ETAL 3,175,788

AIRCRAFT CONTROL APPARATUS 13 Sheets-Sheet 13 Filed July 23, 1958 AT ORNEY 3,175,788 AinonArT ooNTaoL APPARATUS I John Baldwin, Toronto, Gntario, Canada, Henry W.

Berry, Largo, Him, and Robert M. Madvig, Bloomington, Minm, assignors to Honeywell Inc, a corporation of Delaware Filed July 23, 1%8, Ser. No. 751,597 4 Claims. (Cl. 24477) This invention relates to the field of aviation, and more specifically to aircraft control in elevation to follow a desired path, sepecifically the nonlinear approach path used in bringing aircraft to land on the deck of an aircraft carrier at sea. 'The general system is shown in the copending application of Baldwin et al., Serial No. 751,594, filed July 23, 1958, now Patent No. 3,053,487. Control of the aircraft in azimuth is also included in the overall system, and apparatus for thatpurposc is more specifically disclosed in the copending application of Berry et al., Serial No. 751,596, filed July 23, 1958, now abandoned. Both of these copending applications are assigned to the assignee of the present application.

The apparatus embodying the present invention includes a carrier-based portion and an airborne portion, and is used during the final phase of an automatic landing during which the aircraft is observed by a precision radar which gives outputs representative of the altitude and closing speed of the aircraft and of its abscissa and ordinate on a'set of Cartesian axes having its origin at the touchdown point and its axis of ordinates aligned with the landing strip on the carrier.

An azimuth computer corrects the two last named outputs for parallax between the location of the touchdown point and the location of the precision radar antenna, and controls the aircraft in azimuth through a radio command link and an automatic pilot in accordance with the parallax corrected signals, to maintain the aircraft on a predetermined nonlinear path in azimuth. At first the aircraft is maintained at a predetermined constant altitude.

A vertical computer receives the first two signals from the precision radar, and the parallax corrected ordinate signal from the azimuth computer, and controls the aircraft in elevation in accordance therewith through the radio command link and the automatic pilot, to maintain the aircraft on a predetermined nonlinear path in elevation, supplanting the constant altitude control.

Safety measures include disabling the airborne control system unless the landing flaps of the aircraft are down, and restoring control of the aircraft to the human pilot if the radio command link fails, if the precision radar loses lock on, if the aircraft departs too widely from the predetermined path, or if it ever goes below a predetermined minimum altitude prior to its final descent.

It is a primary object of this invention to provide new and improved apparatus for controllingthe flight of an aircraft in elevation. Other-objects are to control an aircraft in elevation in accordance with observations of its position taken at a carrier or ground station, and to provide means for automatically controlling an aircraft to follow a nonlinear path in elevation with respect to such observations. Further broad objects are to compute at the carrier the proper time for an aircraft to begin its final approach to landing in viewof the altitude error of the aircraft and the most probable elevational error of the carrier deck at the instant of touchdown, and toprovide a smooth transition from level'fiight to flight at a desired glide angle for various initial altitudes of the aircraft;

Various other objects, advantages, and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and objects attained by its use, reference should be had to the subjoining drawing, which forms a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention In the drawings, FIGURE 1 is a general block diagram of the vertical aircraft control system comprising the subject matter of the invention, FIGURE 2 is a diagram showing the vertical path of an aircraft using the inventive system, FIGURE 3 is a detailed enlargement of the final portion of FIGURE 2, FIGURE 4 is a more detailed block diagram of the general system, FIGURE 5 is a block diagram of a'vertical coordinate translator comprising a portion of the invention, FIGURE 6 is a circuit diagram of an altitude analog or H(t) computer which is a portion of the vertical coordinate translator, FIGURE 7 is a circuit of a comparator used in the vertical. coordinate translator, FIGURE 8 is a circuit diagram of a tip range computer used in the control system, FIGURE 9 is a functional diagram of a deck predictor used in the apparatus, FIGURE 10 is a circuit diagram of a vertical signal transfer control used in the practice of the invention, FIGURES 11 and 12 are diagrams of comparator circuits used in the equipment, FIGURE 13 is a wiring diagram of the control circuit of the carrier based equipment, FIGURE 14 is a functional diagram of the radio command link, FIGURE 15 is a circuit diagram of the elevator channel of an automatic pilot as used in the practice of the invention, FIGURE 16 is a circuit diagram of an airspeed compensator which comprises a portion of the automatic pilot, FIGURE 17 is a circuit diagram of an altitude control which comprises a portion of the automatic pilot, FIGURE 18 is a circuitdiagram of a vertical coupler which is used in the practice of the invention, and FIGURE 19 is a wiring diagram of the control circuit of the airborne equipment.

The general character of the vertical control system of the invention is dictated by the specialized conditions surrounding the final approach of an aircraft to touchdown on the deck of a carrier. It has been found preferable to make all of the initial approach at a constant altitude, but for flexibility of operation it is desirable to have a range of altitude anywhere within which the system is operaable. It has also been found preferable not to make the landing a single sloping straight line, but rather to descend to an altitude of about twenty-five feet above the carrier deck, level out to'establish a stable aircraft attitude, and then make the final descent. One of the advantages of this two step procedure is that it shortens the prediction time required of a deck position predictor and hence increases its accuracy. Another advantage is that it delays until the last possible moment the instant at which the aircraft is committed to a landing, and thus decreases the interval during which unexpected occurrences can endanger the safety of the landmg.

FIGURE 1 shows the inventive system in its broadest form. Carrier based radar equipment 26 supplies to computers 21 signals 22 representative of the location of the aircraft in elevation and azimuth, and of its closing speed. Computers 21 derive from signals 22 a second set of signals 23 representative of the actual and desired location of the aircraft in elevation. These signals are supplied to the aircraft through a radio command link 24 including a transmitter 25 and a receiver 26. The outputs 27 from receiver 26 are supplied to an automatic pilot 30 where they control the aircraft.

FIGURE 2 shows the path followed by the aircraft in elevation by the line ABCDEFGHO. Portions AC and 3 FG are straight and level. Portions DE and H are straight, and slope at angles dependent upon the airspeed of the aircraft: the rate of descent along the first is eleven feet per second and that along the second is nine feet per second. Portions CD, EF, and GH are fairing curves. The nominal altitude of the aircraft above the deck of the carrier during the portion FG is twenty-five feet, and that during the portion AC is between one hundred thirty and one hundred ninety feet.

FIGURE 2 may be considered as a plot of altitude above the deck against time before touchdown. The line ED may be extended to some point I at a higher elevation than 200 feet. It is desired that all aircraft landing on the carrier come on to the line I E at some point D between E and J and thereafter follow the exact path DEFG. In order to accomplish this it is necessary that the aircraft begin to depart from its level flight not at the point of intersection of the level line with the line JD, but at some earlier point such that considering the aerodynamic characteristics of the aircraft it will have settled down to descend at a constant rate by the time the line JE is reached. Means for accomplishing this are sup plied, and include means tentatively establishing a line DJ' parallel to DJ and spaced from it by an amount determined by the characteristics of the aircraft in question.

It will be appreciated that, since the distance y of the aircraft from the touchdown point and the speed s of the aircraft are both known, it is possible to compute the time t remaining before touchdown from the well known relation that distance is equal to speed multiplied by time, that is In other words, there is available a continuous source of information as to the length of time before touchdown, and if the desired course in elevation is laid out in units of time before touchdown rather than of distance before touchdown, the same plot can be used for all airspeeds.

FIGURE 3 is an enlarged view of the final touchdown portion of the landing path. The location of point G is determined in the following fashion. The response of a typical aircraft to a step command which orders a constant rate of descent of 9 feet per second is not instantaneous. That rate is achieved in about 2 /2 seconds, during which interval the aircraft has descended five feet. Consequently the time 1 required to descend from any given height h following the slope command can be computed as follows and, for small changes in 11,

Ah At-- (3) For the case where the aircraft is exactly 25 feet above the carrier and the latter is at the standard elevation, the point G is located at a time or 4.72 seconds before touchdown.

Error in the aircraft altitude and deviation of the predicted deck position from the standard elevation can both occur, and both of these factors influence the time at which the final tip signal must be given. If the carrier deck is to be lower than normal at the touchdown instant, the total time of descent is greater, and the final tip signal G must be given :at t earlier than t but if the carrier deck is to be higher than normal at the touchdown instant, the total time of descent is less and the final tip signal G must be given at 1 later than t Similarly, if the aircraft is higher than normal, the total time of descent is greater and the final tip signal G must be given at t earlier than t but if the aircraft is lower than normal the total time of descent is less and the final tip signal 6.; must be given at t later than t Means for making these adjustments in the time of final tip are included in the invention disclosed below.

FIGURE 4 shows the system in more detail. The carrier based precision radar 31 receives signals from its antenna 32 and automatically tracks the aircraft in azimuth by operation of the rotator 33. As suggested at 34 the precision radar is initially slaved to a marshalling radar in the overall system, to enable the precision radar to be set on a particular aircraft, but this forms no part of the present invention. Radar 31 is shown as providing an altitude output 35, a speed output 36, y and x outputs 3'7 and 4t, and a lock on output 41 which is present whenever the radar is automatically tracking ain aircraft.

Also included in the carrier based equipment is an azimuth computer 42, disclosed completely in the second application referred to above, and a vertical computer 43 which includes a vertical coordinate translator 44, a vertical signal transfer 45, a tip range computer 46, and a deck position predictor 47. The translator 44 computes, from speed output 36 and from the parallax corrected ordinate or distance signal 54) supplied through azimuth computer 42, the time t remaining before touchdown. A path analog in n'anslator 44 gives a signal representative of the scheduled altitude of the aircraft for the time t, and this is compared with the altitude output to supply a control output 51 to signal transfer control 45 which represents the altitude error of the aircraft. Transfer 45 converts the error output 51 to a signal 52 suitable to modulate the transmitter of radio command link 24. A signal 53 representative of the actual altitude of the aircraft is also transmitted to transfer 45, and the latter gives a wave-off signal at 54 if the aircraft ever goes below a predetermined minimum before final tip altitude, or if it departs upwardly or downwardly from the scheduled path by more than a predetermined amount.

The details of predictor 47 are not material to the present invention, but for completeness one suitable predictor is described below. The predictor functions to supply at 55 a signal representative of the most probable displacement of the touchdown point from the standard elevation at the instant of touchdown. In tip range computer 46 this signal is combined with signals 56 and 57 representative of the altitude error of the aircraft and its speed, an an output 60 is supplied to translator 44, but this output is not supplied until the time before touchdown decreases to a predetermined value. For determination of this a signal 61 representative of the actual time to touchdown as computed in translator 44 is supplied to computer 46 for comparison with a fixed signal.

The azimuth control signals from computer 42 to command link 24 are suggested at 62 and 63. The portion of FIGURE 4 to the left of the broken line AA represents carrier based equipment, while the portion of FIGURE 4 to te right of the broken line represents airborne equipment.

In the airplane the receiver of radio command link 24 supplies an altitude error signal 64 to a vertical coupler 65, and further signals 66 and 67 are supplied to coupler from an altitude control 70 and an airspeed compensator 71. A wave-off signal 72 from command link 24 is also used as will be described in connection with FIG- URE 19.

The automatic pilot of the aircraft, which receives signals 78 from air speed compensator 71 is shown by the general reference numeral 76 and includes sensing elements 77 giving signals to summing circuits and amplifiers indicated at 80 to actuate the control surfaces of the aircraft: the elevators 81 are controlled through a circuit 32, for example. Vertical coupler 65 supplies a pair of signals 87 and 90 which are used in the control of the elevator, as will be discussed in connection with FIGURE 15.

FIGURE 5 is a somewhat more detailed showing of the vertical coordinate translator 44. The altitude, speed,

and distance signals 35, 36, and 50 are supplied to the fixed contacts 920 and 92 and 92j respectively of a relay 92 which may be energized to actuate movable contacts 92a, 92a, and 91- into engagement with the fixed contacts just named and out of normal engagement with fixed contacts 92b, 92e, and 92h, all respectively. Fixed contact 921) is connected to an initial h set device 93. Fixed contact 92s is connected to an initial s set device 94. Fixed contact 92h is connected to an initially set device 95. Devices 93, 94, and 95 are energized from a common source 96 of alternating voltage of a selected frequency. y

Relay contact 924 is connected to suppiy a first, electrical input 97 to anelectromechanical multiplier 100, having a second mechanical input on the shaft 101 of a motor 102, and having an electrical output 163, Relay contact 92g is connected to supply an input 192 to an adder 165 which has as further inputs the output 193 from multiplier 1G0, and the signal 60 from tip range computer 46: initially this last signal is Zero.

6 driven through a shaft 186 by a motor 187. Motor 187 has limit switches, not shown, and'may be driven in either'direction by a suitable electrical energization'of The signal 106 of adder 105 is fed to a motor control amplifier 107 which energizes motor 102 from source 96 through acable 110 under the control of signal 106.

As is well known, the product of'speed multiplied by time is distance. Output 103 from multiplier 100 is the product of speed and shaft rotation, and is fed back to adder 195. Amplifier 197 energizes motor 162 to run until adder input 1113 becomes equal'to input 194. Then the product of speed and shaft rotation has been made equal to distance, and the shaft rotation is therefore time. Since the input 104 is proportional to distance of the craft from the touchdown point, the time represented by shaft 101 is time before touchdown.

Shaft 101 of motor 102 also drives a path analog 111 to give an output 112 which is a predetermined nonlinear function of shaft rotation, and is repesentative of the land: ing path shown in FIGURE 2. Analog 111 is energized from source 96, and is shown in more detail in FIGURE 6. It comprises first and second voltage dividers 113 and 114 including sliders 115 and 116, driven by shaft 101, and windings 117 and 124). Each winding has a total length of 357 degrees, and is tapped at each 15 degrees from 60 to 150'degrees. Thus winding 117 is tapped at 121, 122, 123, 124, 125, 126, and 127 and winding 120 is tapped at 130, 131, 132, 13 3, 134, 135, and 136. The windings and sliders are arranged in staggered relationship, so that when slider 16 is at the 90 degree tap on winding 120, for example, slider 115 is half way between the 75 degree'and 90 degree taps on winding 117. The

windings are energized in parallel from a pair of con ductors 137 and 140, a fixed resistor 141 being connected in series between winding 117 and conductor 137, and a fixed resistor 142 being connected in series between winding 120 and conductor 140. Characterization of the output from the voltage dividers is accomplished by resistors shunted across the taps on the windings: resistors 143, 144, 145, 146, 147, 148, and 149 are associated with winding 117, and resistors 152, 153, 154, 155, 156, 157 and 169 with winding 120. Resistors 145, 146, 147, 155,

156-, and 157 are short circuits of essentially zero resistance.

Analog 111 is energized from source 96 through a transformer 161 having a primary winding 162 and a secondary winding 163. Connected across secondary wind-' ing 163 is a series circuit made up of the fixed resistor 16 1, the winding 165 of a voltage divider 166 having a "slider 167, 'andthe winding 179 of a voltage divider 171 having'a slider 172. The upper terminal of winding 170 is connected to conductor 137 by conductor 173. Slider 172 is. adjustable by a manual knob 174 and is grounded an amplifier 229, the last stage 221 of which has alterconductors 190, 191, and 192 under the control of relay contacts 193a, 1931), and 193c and relay contacts 194a and 194-0. Movable contact 193a normally engages fixed contact 19311, but may be operated to disengage contact 193b and to instead engage contact 1936'. Movable contact 194a may be operated to engage fixed contact 19 1c. Conductor 191 is connected to fixed contact 1931b and conductor 192 is connected to fixed contact 1940. Movable contact 194iz is connected to fixed contact 1930 by conductor 195. Movable contact 193a is connected to conductor 196, and conductors 190 and 196 are connected to source 96. Thus motor 187 is energized and o erates until one of the limit switches is actuated: at this time slider is at the left hand end of winding 183.

Turning again to FIGURE 5, relay contact 92a is shown as connected at 197 to a parallax corrector 266 which may be energized from source 96. The parallax corrected 12 output 251 from corrector 260 is supplied at 53 for transmission to the signal transfer control, and also at 252 to comprise an inputto a summing amplifier 233. A second input 294 is supplied to amplifier 203 from the movable relay contact 194d, which normally engages fixed contact 194:: connected to a rebalance signal device 265 energized from source 96 and adjusted through a shaft 256 by a servo 207. Fixed contact 194 which movable contact 194d engages instead of fixed contact 1194s when the relay is energized, is connected at 210 to receive the path analog output 112. Shaft 266 of servo .297 also adjusts an altitude signal device 211 energized from source 96, which supplies a first signal 212 to a comparator 213. A second signal 214 is supplied to the comparator from path analog output 112.

Comparator 213 operates to energize relay 194 whenever input 214 is less than input 212, and a suitable arrangement for accomplishing this is shown in FIGURE 7. Inputs 212 and 214 are supplied through a pair of summing resistors 215 and 216 to the input stage 217 of nating plate energization from source 96. A relay 269 is in the plate circuit of the last stage. Until the signal 2114 becomes less than the signal 212, the grid of output stage 221 is negative whenever the anode is positive, and no appreciable plate current flows. When signal 214 becomes less than signal 212 the grid voltage and anode voltage on stage 221 are in phase, and relay 209 is energized. As shown in FIGURE 13, this energizes relay 194.

' Servo 267 of FIGURE 5 is energized with the output 51 of summing amplifier 203, through an isolating resistor 222, and is grounded at 224 when movable relay contact 479a engages fixed relay contact 4790. Thus the normal operation of servo 207 in combination with amplifier 203 is to keep devices 2115 and 211 adjusted to the actual altitude of the aircraft. Until the latter comes quite near the carrier the quantity y has a large value and the H(t) output 214 from analog 111 is comparator 213 is greater than any output 212 obtainable from device 211. When the input 214 becomes less than input 212, comparator 213 energizes relay 299 and hence relay 194, and the output from path analog 111 is substituted for that from device 295 as the second input to summing amplifier 203. The latter can no longer balance itself by operation of motor 267, and the output 51 becomes the altitude error E instead of zero.

in the right central portion of FIGURE 5 the shaft 161 of motor 192 is shown extended to drive a pair of movable contactors 225 and 226, the former with respect to a pair of fixed arcuate contacts 227 and 230 and the latter with respect to a pair of fixed arcuate contacts 231 and 232. The arcuate space between contacts 231 and 232 is occupied by a resistance winding 233 connected to the contacts and arranged to be engaged by contactor 226: the same space between contacts 227 and 230 is empty so that contactor 225 makes no contact. Conductors 2 34, 235 and 236 leading to elements 225, 227, and 230 are also shown in FIGURE 13. Contact 231 is grounded. Contact 232 is connected to source 96 by conductor 237. Contactor 226 is connected by conductor 240 to fixed relay contact 24111 normally engaged by movable contact 241a, which may be operated to disengage contact 24111 and to engage instead fixed contact 2410. Movable contact 241a supplies input 61 to tip range computer 46. Fixed contact 2410 is connected by conductor 242 to source 96.

Initially y is so large that t computed by motor 102 and multiplier 100 results in rotation of shaft 101 to an extent which puts contactors 225 and 226 at the counterclockwise ends of contacts 227 and 232, and which puts sliders 115 and 116 at the upper ends of windings 117 and 120. As the aircraft nears the carrier y decreases, so that t decreases and the contactors rotate in a clockwise direction and the sliders move downwardly. Elements 227 and 232 are so dimensioned that the contactors 225 and 226 move off them at the point B, FIG- URE 2, and contacts 230 and 231 are so proportioned that the contactors engage them at point G, for a landing when the aircraft is exactly 25 feet above the carrier during the portion GF and when the carrier is to be exactly at the standard elevation at touchdown. It is apparent that contactor 226 has a constant voltage until point F is reached, and that this voltage decreases linearly to zero by the time G is reached. This voltage constitutes the time-to-tip signal, for tip range computer 46, as long as relay contacts 241a and 2411) are in engagement.

Tip range computer 46 has as a principle function to supply a signal 60 for modifying the instant at which the point G, FIGURE 2, occurs. Referring to FIGURE 8, computer 46 is seen to include a cathode follower 243 to which the altitude error signal E, at 56 is supplied, and from which a signal 244 is derived through a gain adjustor 245 and fed through a summing resistor 246 to summation point 247. Also supplied to point 247, through a summing resistor 250, is the deck error signal Ah at 55, from deck predictor 47. Summation point 247 is connected to a motor control amplifier 251. The signals are so chosen that a signal at 56 representative of a position of the aircraft above a standard 25 foot altitude has the same effect in amplifier 251 as does a signal at 55 representative of a position of the deck below the standard elevation.

Amplifier 251 energizes a motor 252, through a cable 253, and the shaft 254 of the motor adjusts a rebalance device 255 which supplies a further signal to point 247 through summing resistor 256. The position of shaft 254 is thus a measure of the total vertical distance to be traveled by the aircraft in coming to rest on the carrier, and the shaft is extended to adjust the slider 257 of a voltage divider 260 having a winding 261. Motor 252 runs to a position in which its shaft 254 has been rotated in proportion to (E -Ah), which vertical distance is proportional to At so that the rotation of shaft 254 is a measure of At.

Since I is computed in the vertical coordinate translator on the basis of y, the correction in time required (At), must be converted into terms of distance. This can be done by multiplying At by s. To accomplish this the s signal at 57 is fed through a cathode follower 262 and a gain adjuster 263 to one end of the series circuit 264 including a resistor 265, the winding 261 of voltage divider 260, a variable resistor 266, a fixed resistor 267, and a capacitor 270. Adjuster 263 is also connected to the input of an inverting amplifier 271 whose output is connected to capacitor 270. Thus the lower end of Winding 261 is at a potential with respect to ground which is proportional to +s, and the upper end is at a potential with respect to ground which is proportional to s. Proper selection of resistance values and suitable adjustment of variable resistor 266 make the two constants of '8 proportionality the same. The motor and slider are set so that the slider is at ground potential when E Ah equals zero. Therefore movement of the slider in opposite directions gives values of Ay of opposite sense, as is required.

The Ay signal on slider 257 is connected to fixed relay contact 2720: fixed contact 272k is grounded, and movable relay contact 272a, which normally engages fixed contact 2721; but may be operated to engage fixed contact 2720 instead, is connected to supply output 60 to adder of FIGURE 5.

As has been previously pointed out, the details of deck predictor 47 are not a part of the present invention. However, for completeness FIGURE 9 is presented to show schematically one form of predictor Which is suitable for this use. The figure is in REAC diagram form, since this presentation emphasizes the functional characteristics of the equipment. The elements identified by numerals 273, 274, 275, 276, 277, 280, 281, 282, 283, 284, 285, and 286 are summing amplifiers with a gain of 1. The elements identified by numerals 287, 290, 2511, 292, 293, 294, 295, 296, 297, 300, 301 and 302 are integrators having the characteristic of giving one volt per second output for a one volt input. The elements identified by numerals 303, 304, 305, 306, 307, 310, 311, 312, 313, 314, 315, 316, 317, 320, 321, 322, 323, 324, 325, 326 and 327 are voltage dividers having resistances of 30,000 ohms, and set at the following decimal fractions of full value.

Voltage divider 303 is a calibrating adjustment and is set when the equipment is installed.

The inputs to the grids of the amplifiers or integrators are through 1 megohm summing resistors, except that the input to amplifier 273 and the signals from dividers 307 and 325 are through 10 megohms, and the signals from dividers 314, 316, and 317 are through 4 megohms, as are both signals into integrator 302.

The output 55 from the predictor of FIGURE 9 has been found to represent within an error of i1 foot the departure of the carrier deck from its standard elevation at a time 6.5 seconds subsequently.

FIGURE 10 shows signal transfer control 45 in more detail. The altitude error signal E from coordinate translator 44 is supplied at 51, and is connected to fixed relay contact 3300. Movable relay contact 330a normally engages fixed relay contact 330]) which is grounded, but may be actuated out of engagement with contact 33Gb and into engagement with fixed contact 330C.

Movable contact 330a is connected by conductors 331 and 332 to a bridge network 333 having input terminals 334 and 335 and output terminals 336 and 337, the latter comprising the sliders 340 and 341 of a pair of voltage dividers 342 and 343 having windings 344 and 345 which form the arms of the bridge network. Input terminals 334 and 335 are energized with alternating voltage from the secondary winding 346 of a transformer 347 whose primary winding 350 is connected to source 96. Slider 340 is adjustable by a manual zero adjuster knob 3-51. Slider 341 is adjusted by the shaft 352 of a motor 353, and is connected to energize an amplifier 354 through a filter 355. Amplifier 354 comprises a pair of triodes 356 and 357 which are cathode coupled by a common cathode resistor 360. The signal from filter 355 is applied to the grid of triode 356, and the signal from a velocity generator or dynamic transformer 361 driven by motor 353 through shaft 352 is applied to the grid of triode 357. The output of amplifier 354 appears at 362 and is representative of the sum of the two grid signals: it is supplied to a motor control amplifier 363 which energizes motor 353 through a cable 364 to operate in either one direction or the other,,according as amplifier 363 has an input of one phase or the other. Operation of motor 353 adjusts slider 341 to unbalance bridge 333 by an amount equal and opposite to the signal 51, so that the rotation of shaft 352 is a measure of signal 51. Velocity generator 361 is energized from source 96 and supplies an antihunt signal.

A phase shifter 365 is shown as driven by shaft 352 and as having an input cable 366 and an output cable 367. This arrangement is discussed more fully in connection with FIGURE 14. The signal on cable 357 comprises output 52 shown in FIGURE 4.

Also shown in FIGURE 10 are comparators 370, 371,

and 372, which are like comparator 213 of FIGURE 5.

Included in comparator 370 is a relay 373 which may be energized to displace a movable contact 373a into engagement with a fixed contact 373c. Included in comparator 371 is a relay 374 which may be energized to displace a movable contact 374a into engagement with a fixed contact 3740. Included in comparator 372 is a relay 375 which may be energized to displace a movable contact375a into engagement with a fixed contact 3750. nected to a first common conductor 464, and fixed contacts 373a, 374a, and 37510 are connected to a second common conductor 460, as shown in FIGURE 13. Con- .ductors 464 and 460 comprise output54 of signal transfer 45.

FIGURE 10 also'shows by the general reference numeral 385 a source of standard voltages for comparators 370, 371, and 372, including a transformer 351. having a primary winding 382 connected to source 96 and-a pair of secondary windings 383 and 384 connected in series by a grounded conductor 385 at terminals 386 and 387. Connected between terminals 356 and 390 of winding 383 is a fixed resistor 351 in series with the parallel combination of two series circuits, the first including the windings 392 and 393 of a pair of voltage dividers 394 and 395 having sliders 396 and 397, and the second including a fixed resistor 409 and the winding 451 of the Voltage divider 452 having a slider 403. Connected between terminals 387' and 404 of winding 354 is a'fixed resistor 455 in series with the parallel combination of two series circuits, the first including a fixed resistor 456 and a winding 457 of the voltage divider 410 having a slider 411., the second including a fixed resistor 412 and the winding 413 of a voltage divider 414 having a slider 415.

. Slider 397 supplies a'signal through conductor 416 to comparator 372 representative of the floor or minimum altitude below which the aircraft must never descend under automatic control until the point G is reached. Sliders 3% and 453 are connected by conductors 417 and 425 to fixed relay contacts 42% and 421C, the former being normally engaged by a movable relay contact 421a connected to comparator 370 by conductor 422. Sliders 411 and 415 are connected by conductors 423 and 424 to fixed relay contacts 421a and 421i, the former being normally engaged by a movable relay contact 421d, con-,

nected to comparator 371 by conductor 425. It will be evident that the signals supplied on conductors 422 and 425 are opposite in phase, and these signals represent the limits of the upward and downward aircraft deviation from the desired path. The permitted deviation of the aircraft is greater when the relay contacts are as shown, and is reduced when relay 421 is energized.

An arrangement generally similar to that just described also makes up a part of tip range computer 46, as is better shown in FIGURE 11. A comparator 426 is shown as receiving input 61, FTGURE 5, and also a Movable contacts 373a, 374a, and 375a are con is energized from A.C. source 96.

standard signal 427 derived from the slider 43s of a voltage divider 431 whose winding 432 is energized, in series with a fixed resistor 433, from the secondary winding 434 of a transformer 435, the primary winding 436 of which Normally signal 63 is larger than signal 427. When signal 61 decreases to become equal to signal 427, comparator 426 energizes a relay 437, bringing movable contact 437a into engagement with a fixed contact 4370. The function performed by relay 437 will be described below.

The same sort of arrangement comprises a portion of the control system of the carrier based equipment,'as is described in detail in the second copending application referred to above, and as is shown schematically in FIG- manual wave-oif switch 455 and conductor 456.

URE 12. A comparator 445 is shown as receiving input "5, FTGURE 4, and also a standard signal 441 derived from a suitable device 442 energized from A.C. source 56. Initially signal 55 is greater than signal 441. When signal 59 decreases to become equal to signal 441, comparator 445 energizes a relay 443, bringing a movable contact 443a into engagement with a fixed contact 4430. The function of relay 443 will also be discussed below.

The control circuit for the carrier based equipment is shown in FIGURE 13, and is energized from A.C. source 56. When a power switch 444 is closed, power is sup-' plied through a fuse 445 to a power bus 446, and the ground bus is shown at 447.

The Winding of relay 482 is energized with signal 41 of FTGURE 4, as shown to the left of FIGURE 13.

One side of wave-off relay 450 is grounded through conductor 451: the other side may be connected to power bus 446 through fivedhferent circuits. The first circuit includes conductors 452, 453, and 454, a normally open The second circuit includes conductors 452, 453, and'457, normally closed relay contacts 241e and 241d, conductors 465, 461, and 462, normally open relay contacts 373s and 373a of comparator 375, conductors 4.63 and 464, a normally closed ready switch 465 and conductor 466. The third circuit includes conductors 452, 453, and 457, relay contacts 241s and 24103, conductors 465, 461, and 467, normally open relay contacts 3740 and 374a of comparator 371, conductors 475, 471, and 464, ready switch 465, and conductor 466. The fourth circuit includes condoctors 452, 453, and 457, relay contacts 241a and 241d, conductors 465 and 472, normally open relay contacts 37 5c and 375a of comparator 372, conductors 473, 474, 471, and 464, ready switch 465, and conductor 456. The fifth circuit includes conductors 452 and 475, normally open relay contacts 456a and 455a, conductors 476, 474, 471, and 464, ready switch 465, and conductor 456.

Q One side of a transfer start relay 477 is grounded through conductor 48%. The other side may be connected driven by a motor in response to radar signals, to be positioned in accordance with the distance of the aircraft from the touchdown point, and contactor 4% rotates clockwise with decreasing distance: it engages segment 487 when the distance is about 1950 yards, all as described in the second copending application referred to above.

One side of a transfer end relay' 479 is grounded through conductor 47%. The other side may be connected to power bus 446 through conductor 48%, normally open relay contacts 4'77 and 477a, and conductor 439.

One side of an amber signal light 493 is grounded through conductor 494. The other'side may be connected to powerbus 446 through conductor 495, normally open relay contacts 459] and 455d, and conductor 496.

Stand-by relay windings 52 and'l93 are connected in parallel by conductors 497 and 5%. One side of the relays can be grounded through conductor 551, normally 11 open relay contacts 443a and 4430 of comparator 440, and conductor 502. The other side of the relays can be connected to power bus 446 through conductor 563, normally open relay contacts 482) and 432d, conductor 564, normally closed relay contacts 456g and 45611, and conductor 595.

One side of a rescind relay 566 is grounded through conductor 567. The other side may be connected to power bus 446 through conductor 235, segment 227 and contact 225 of a commutator switch 511, conductor 234, normally open relay contacts 193g and 155;, and conductor 517. Shaft 161 is operated by motor 102 as described in connection with FIGURE 5.

One side of a green signal lamp 520 is grounded through conductor 521. The other side is connected to power bus 446 through conductor 522, normally closed relay contacts 193:2 and 193d, and conductor 523.

One side of a blue signal lamp 524 is grounded through conductor 525. The other side may be connected to power bus 446 either through conductor 526, normally open relay contacts 193i and 193m, and conductor 523, or through conductors 526, 527, and 530, normally open relay contacts 194j and 194g, conductors 531 and 532, normally open relay contacts 265:: and 265a of comparator 213, and conductor 533.

One side of a final tip relay 241 is grounded through conductor 534. The other side may be connected to power bus 446 through three different circuits. The first circuit includes conductor 535 and 236, segment 236 and contactor 225 of commutator switch 511, conductor 234, relay contacts 193g and 193i, and conductor 517. The second circuit includes conductors 535 and 537, normally open relay contacts 241g and 241 conductors 540 and 527, relay contacts 193 and 193d, and conductor 523. The third circuit includes conductors 535 and 537, relay contacts 241g and 241 conductors 546 and 536, relay contacts 194 and 194g, conductors 531 and 532, relay contacts 2090 and 265a of comparator 213, and conductor 533.

A servo lock relay 541 is connected in parallel with final tip relay 241 by conductor 542 and grounded conductor 543.

One side of nose down relay 194 is grounded through conductor 544. The other side may be connected to power bus 446 either through conductors 545 and 532, relay contacts 209c and 209a of comparator 213, and conductor 533, or through conductors 545 and 5351, relay contacts 194g and 194 conductors 530 and 527, relay contacts 193i and 193d, and conductor 523.

The energizing circuit for motor 187 of FIGURE 6 appears again in FIGURE 13. The motor is shown to comprise a pair of windings 546 and 547 having a common terminal 550, grounded through conductor 196, and a pair of individual terminals 551 and 552 joined by a capacitor 553. Terminal 551 may be connected to power bus 446 through conductor 554, a normally closed limit switch 555, conductor 191, normally closed relay contacts 19% and 193a, and conductor 156. Terminal 552 may be connected to power bus 446 through conductor 556, normally closed limit switch 557, conductor 192, normally open relay contacts 1940 and 194a, conductor 1155, relay contacts 1930 and 193a, and conductor 196.

One side of a precision relay 334 is grounded through conductor 56%. The other end may be connected to power bus 446 through conductor 561, normally open relay contacts 447m and 477k, and conductor 562.

One side of an error limits relay 421 is grounded through conductor 564. The other side may be connected to power bus 446 through conductor 565, normally closed relay contacts 506k and 566a, and conductor 566.

One side of a Ay relay 292 is grounded through conductor 567. The other side may be connected to power bus 446 either through conductors 570 and 571, normally open relay contacts 4370 and 43% of comparator 426, and conductor 572, or through conductor 570, normally 7.2 open relay contacts 272 and 272d, conductor 573, normally open relay contacts 193k and 192m, and conductor 574.

FIGURE 14 is a schematic showing of the radio command link 24 in considerable functional detail. Transmitter 25 appears at the left of the figure and receiver 26 appears at the right. In the transmitter a cycle generator 575 is shown as supplying a first output 576 to a first modulated oscillator 577, and a further output 366 to phase shifter 365. Phase shifter 365 has already been discussed in connection with signal transfer control 45 of FIGURE 10, and is shown to be adjusted by motor shaft 352. The output of the phase shifter is a 90 cycle alternating voltage whose phase relative to that supplied by generator 575 is representative of the rotation of the phase shifter shaft, that is, of the vertical error of the aircraft for phase shifter 365. This output 367 is supplied to a further modulated oscillator 530, and the oscillators supply, to a mixer 5S1, modulated outputs 582 and 583, all respectively.

In order that the various signals may later be separated, the oscillators operate at distinguishable frequencies. While any suitable modulating arrangement may be used, it has been satisfactory in practice for oscillators 577 and 580 to be phase shift modulated at a shift frequency of 90 cycles per second, the 90 cycle modulating voltage being shifted in phase proportional to the operation of shaft 352 and phase shifter 365. In the embodiment of the invention referred to above the frequency of modulated oscillator 577 shifts between 19.7 and 20.2 kilocycles per second, and that of oscillator 580 shifts between 14.1 and 14.6 kilocycles per second.

FIGURE 14 shows a plurality of keyed oscillators 584, 585, 586, and 537. Each of these oscillators operates at one of two frequencies accordingly as a control circuit for the oscillator is open or closed. The control circuits of these oscillators are controlled by the operation of certain relays, the windings of which are energized as shown in figures previously described. Thus oscillator 584 operates at a first frequency unless relay contacts 450k and 45621 are in engagement. Oscillator 585 operates at a first frequency unless both relay contacts 477g and 477i and relay contacts 47%! and 479:: are in engagement. Oscillator 586 operates at a first frequency unless both relay contacts 506d and 506 and relay contacts 194k and 19411 are in engagement. Oscillator 587 operates at a first frequency unless relay contacts 241k and 24111 are in engagement.

The frequencies of oscillators 584, 585, 586, and 587 are mutually distinguishable, and are also distinguishable from the frequencies of oscillators 577 and 580: oscillator 584 operates at 2.9 or 3.1 kilocycles per second, oscillator 585 at 3.9 or 4.1 kilocycles per second, oscillator 586 operates at 4.9 or 5.1 kilocycles per second, and oscillator 587 operates at 5.4 or 5.6 kilocycles per second, in the embodiment of the invention found satisfactory.

A mixer 590 is connected to receive the signals 591, 592, 593, and 594 from oscillators 584, 586, 587, and 5%, respectively.

Mixers 581 and 590 may include such isolation stages as are required to prevent interaction between the various signals supplied thereto: their outputs 595 and 596 are supplied to a further mixer and amplifier 597 which supplies to a further modulator 669 an input 6431 which includes both the proportional signals and all thekeyed signals. Modulator 66th supplies a signal 602 to and may comprise a part of transmitter 663, and there is radiated from the antenna 664 a radio frequency carrier, phase modulated with the intelligence to be transmitted. In one form of the invention a carrier frequency of 235.4 megacycles per second was found satisfactory.

This completes the description of the carrier based portion of the apparatus. In the aircraft the carrier is pick-ed up by receiving antenna and supplied to receiver 666 which amplifies it and demodulates it to l3 remove the carrier. Reception of a signal at an acceptable level supplies an output from receiver 606 along a conductor 607 to operate a switching device 668, the relay contacts 610a and 6100 of which also appear in FIGURE 19. The complex audio signal is supplied at 611 to an amplifier 612. The output 613 of amplifier 612 contains the proportional and switching information in the form of signals of diiferent frequencies, and is supplied to a plurality of sharply tuned band pass filters 614, 615, 616, 617, 626 and 621; Filter 614 passes V frequencies in a narrow band centered at about 19.95

kilocycles per second and supplies a signal 622 determined by the reference signal 576 and comprising a 90 cycle voltage of fixed phase.

Filter 615 passes frequencies in a narrow band centered at 14.35 kilocycles per second, and its output 623 is supplied to a phase detector 624 with the signal 622 from filter 614. The output 625 from detector 624 is a direct voltage which varies in magnitude and reverses in polarity with the amount and direction of the displacement of phase shifter 365: it comprises output 64 of FIG- URE 4.

Filter 616 passes frequencies in a narrow band centered at about 3.0 kilocycles per second and its output 626 is supplied to a detector 627 which energizes the winding of a relay 630 having normally closed contacts 630a and 6301) which open when oscillator 584 is keyed.

The conditionof relay contacts 630a and 63012 comprises signal72 of FIGURE 4.

Filter 617 passes frequencies in the narrow band centered at about 4.0 kilocycles per second and its output 631 is supplied to a detector 632 which energizes the winding of a relay 633 having normally open contacts 633a and 6330 which close when oscillator 585 is keyed.

Filter 629 passes frequencies in a narrow band centered at 5.0 kilocycles per second, and its output at 634 is supplied to a detector 635 which energizes a relay 636 having normally open contacts 636a and 636C which close when oscillator 586 is keyed.

Filter 621 passes frequencies in a narrow band centered at 5.5 kilocycles per second, and its output 637 is supplied through a detector 649 which energizes the winding of a relay 641 having normally open contacts 641a and 6411c which close when oscillator 587 is keyed.

FIGURE 15, to which reference should now be made, shows the vertical control portion of the airborne equipment. An'elevator servornotor 642 is shown as supplying a mechanical output 643 for adjusting the elevators of the aircraft. An elevator position signal device 646 is adjusted simultaneously with the elevators. 7

Motor 642 is energized through a cable 647 by a servo amplifier 650, as will be shown in detail in connection with FIGURE 19. Servo amplifier 650 is energized at 651 from a DC. amplifier 652, energized in turn from a summation point 653 through conductor 654, network 655 and conductor 656.

Theoutput of elevator position signal device 646 is supplied by conductor 657, capacitor 660, and summing resistor 661 to summation terminal 653.

A pitch rate gyroscope supplies an electric signal to the winding 662 of a voltage divider 663 whose. slider .664 is connected by capacitor 665 and summing resistor 666 to terminal 653. A characterizing resistor 667 is connected between slider 664 and winding 662 to give the output of voltage divider 663 a desired nonlinearity.

A complexsignal is supplied to summation point 653 through conductor 671 from. the slider 671 of a voltage divider 672 whose winding 673 is energized from a sec ond summation point 674.

Servo amplifier 650 is shown as also energizing a centering motor 675 through a cable 676: as will be described in connection with FIGURE 19, centering motor 675 is energized alternatively with servomotor 642. Motor 675 adjusts a pitch command signal device 677 through a mechanical connection 630- including a suit- 14 able gear train 681, and connection 680 is extended to carry a manual pitch centering knob 682. Pitch command signal device 677 is connected to supply a signal through conductor 683 and summing resistor 684 to summation point 674.

Further input voltages are supplied to summation point 674 through summing resistors 685 and 686 from a vertical gyroscope, to comprise pitch angle and up-elevator signals, respectively. A further input to summation point 674 may be supplied through a summing resistor 687, which is either. zero or that of a fixed voltage source 630, according as a movable relay contact 691a engages a first contact 63112 or a second fixed contact 691s. The energizing circuit for relay 691 will be described in connection with FIGURE 19.

Two further input voltages are supplied to summation point 674 through summing resistors 692 and 693 from vertical coupler 65 which is shown to comprise a pair of output devices 694 and 695 adjusted by servomotors 696 and 697 through mechanical connections 700 and and a second input 711. Input 71% is derived from conductor 703 through a difierentiator 712, to comprise a rate feedback, so that elements 696, 767, 716, and 712 comprise an integrator. Similarly, servomotor 697 is energized through a cable 713 from a motor control amplifier 714 having output 705 as. a first or feedback input, and having a second input 715. Inputs 711 and 7-15 are derived through an isolation network 716, a connection 717, a compensating network 720, and a conductor 721 from the slider 722 of a voltage divider 723 whose winding 724 is connected by conductor 725 to a movable relay contact 726a, which normally engages a first fixed contact 726b butmay be moved into engagement with a second fixed contact 726c. Contact 7260 is'connected to conductor 625, FIGURE 14, to supply signal 64 representative of the vertical error of the aircraft as determined by the carrier based apparatus. Contact 7261) is connected to receive the signal 66 from the altitude control 70 of the aircraft which signal is representative of the altitude error of the aircraft.

From the foregoing it will be evident that the input to network 655 is the sum of signals representative of the rates of change of elevator position and of pitch attitude, and of pitch command, flap position, and pitch attitude, together with an up elevator signal and, if vertical coupler'65 is engaged, signals representative of the vertical error of the aircraft and its integral based on either radar data or on altitude control data.

Whereas the signals in the carrier based equipment are preferably alternating voltages, those in the airborne equipment are preferably direct voltages, and may be derived from any suitable source.

Sliders 664, 671, and 722 are shown as actuated by a mechanical connection 727, which is operated in accordance with the airspeed of the aircraft. The airspeed ratio control system which performs this adjustment is illustrated in FIGURE 16, to whichreference should now be made.

In FIGURE 16 an airspeed sensor 730, which may be a differential air pressure responsive bellows system, acts through a mechanical connection 731 to displace the slider 732 of a voltage divider 733 with respect to the winding 734. The winding is connected, in series with fixed resistors 735 and 736, across the secondary winding 737 of a transformer 746 whose primary winding 741 is energized from anairborne source 742 of alternating volt- 

1. APPARATUS OF THE CLASS DESCRIBED COMPRISING, IN COMBINATION: MEANS GIVING A FIRST SIGNAL CONTINUOUSLY REPRESENTATIVE TO THE DESIRED ALTITUDE OF AN AIRCRAFT FOLLOWING A PREDETERMINED DESCENT PATH HAVING AT LEAST ONE SLOPING PORTION CONNECTED TO TWO DIFFERENT LEVEL PORTIONS; MEANS GIVING A SECOND SIGNAL REPRESENTATIVE OF THE SLOPE OF SAID SLOPING PORTION; CONTROL MEANS NORMALLY CONTROLLING THE AIRCRAFT IN ELEVATION IN ACCORDANCE WITH SAID FIRST SIGNAL; AND MEANS SUPPLYING SAID SECOND SIGNAL TO SAID CONTROL MEANS IN ADDITION TO SAID FIRST SIGNAL WHILE THE CRAFT IS FOLLOWING SAID SLOPING PORTION OF SAID PATH. 